Ion exchange processes such as softening or demineralization are generally known, where fixed charged sites present on ion exchange materials, such as bead like ion exchange resins, provide sites to bind or store oppositely charged ions and/or particles. These ions and or particles may be exchanged for others existing in solution in a reversible equilibrium process which modifies the ionic composition of the liquid flowing through said ion exchange materials. After the exchange process is completed the process can be reversed by passing a concentrated solution of the original stored ions through the ion exchange medium, eluting the ions or particles exchanged from the solution during exhaustion by replacing them with the original stored ions, and rinsing both the eluted ions and any residual regenerating solution from the ion exchange medium. Once rinsed, the ion exchanger can be placed back into service, again releasing the stored ions in exchange for other ions or charged particles in solution. The exhaustion flow is typically downward, through the ion exchanger, from the top of the ion exchanger and out through the bottom.
To conduct regeneration following exhaustion in the downward direction: it is known to introduce the regenerating solution in the same direction as the exhausting flow, from top to bottom, i.e., in a co-current direction, through the ion exchanger. The regeneration of the ion exchange bed in a co-current direction has considerable drawbacks, as illustrated by the example of the softening of hard water. In this case, hard water flows through layers of ion exchanger material (such as ion exchange resins or zeolite) contained in a vessel (ion exchanger), and the ion exchanger becomes exhausted, or loaded in the flow direction, i.e., from top to bottom, with hardness (principally calcium and magnesium ions). The ion exchange process is equilibrium driven and the final reduction of hardness in the processed water is dependent upon the concentration of hardness ions in the lowermost ion exchange layer (polishing layer), which is the last one through which the water to be treated flows. The lower the residual hardness in the product water, the better the product water quality. During the subsequent regeneration in a co-current system, the hardness ions which are highly enriched in the upper layers of the ion exchanger are eluted from the resin by the regenerating solution and washed downward into the lower layers. In order to generate a good state of regeneration in these lower layers, an excess of regenerating chemical must be employed. This excess is frequently as much as 2 to 3 times the stoichiometric amount required to regenerate the resin depending on the level of hardness required in the product water. This excess amount of regenerating chemical is not utilized and represents a major economic loss both in terms of the cost of the excess regenerating chemical as well as the cost associated with its subsequent disposal.
Introduction of the regenerating solution in an upward direction, opposite to that of the exhausting flow, i.e., in a countercurrent direction, through the ion exchanger is also known. The disadvantage of this process is that the entire bed of ion exchange material, unless fixed or restrained in place by some mechanism, is turned over and mixed together. In particular, the upper layers of ion exchange resins which are most highly charged with hardness are also more dense and are forced from the upper layers to the lower layers as mixing occurs, while the less dense ion exchange material that is still largely uncharged is forced upward from the lower layers to the upper layers. Thus, because of this rearrangement, the situation is similar to the cocurrent operation in that the entire ion exchange bed must be treated with a large excess of regenerating chemical in order to achieve good product quality. The drawbacks in using large excesses of regenerating chemical are the same.
The most efficient use of regenerant and, at the same time, the best product quality is obtained when the ion exchange materials are not mixed or rearranged during counter current regeneration. As a result, the lower most layers of ion exchange materials (or polishing layers) which determine the quality of the product during the charging operation are treated first with fresh regenerating solution and are thus optimally regenerated. Several known systems control this mixing or rearrangement by fixing the bed through the use of either physical restraints or a combination of physical restraints and blocking liquid and or air flows. In each of these methods, the underlying commonality is the need to physically fix or otherwise restrain the ion exchange bed during the regeneration process in order to solve the known difficulties which arise from bed mixing during counter-current regeneration. Each of these known processes has its own known drawbacks and operational problems due to their bed fixing mechanisms.
Another method allows an efficient, counter current regeneration of a non-constrained (not fixed) layered bed without many of the aforementioned problems and is described in allowed U.S. patent application Ser. No. 07/369,238 to Gerhard K. Kurtz filed Jun. 22, 1989 entitled PROCESS AND APPARATUS FOR ION EXCHANGERS, PARTICULARLY FOR REGENERATION AFTER SOFTENING AND DEMINERALIZATION OF AQUEOUS SOLUTIONS, which is incorporated herein by reference. A Kunz counterpart application has issued in the Republic of South Africa as Patent 89/4669 and is also incorporated herein by reference. In this process, as described by Kunz, an ion exchange filter which has been exhausted in a downflow direction is first treated with a regenerating chemical solution and then with a rinse solution, introducing both in a counter current direction, i.e., upflow. This is accomplished by using a series of upward flowing pulses of defined velocity and duration which lift the bed some prescribed distance and are separated by a settle or rest time during which the ion exchange bed returns to substantially its original position without mixing. The essential focus of the Kurtz process is its successful approach to introducing the regenerant chemical without causing significant mixing between the layers of a non-constrained ion exchange bed. This process leads to very efficient utilization of regenerating chemical, and provides the high quality product characteristic of a countercurrent process, since the bed concentration profile is maintained and the lower or polishing layers of the ion exchange bed are always treated with fresh regeneration solution. However, while eliminating the need for various complicated and expensive mechanical apparatus utilized to fix or restrain the ion exchange bed, this regeneration process takes significantly longer than typical operations, thereby limiting its commercial viability.
Accordingly, it is the object of the present invention to overcome the long regeneration time associated with the Kurtz process while maintaining the inherent efficiencies of this process and without re-introducing any of the mechanical design difficulties associated with other previous fixed bed processes.
Specifically, it is the object of the present invention to achieve the rapid, efficient countercurrent regeneration of an unconstrained ion exchange bed in an upward direction with substantially the same amount of regenerating chemical as the Kunz process thereby obtaining a significant savings in both regenerating chemical cost and subsequent associated waste disposal costs without requiring an extended regeneration time.